U.S. patent application number 12/266553 was filed with the patent office on 2009-05-14 for oscillating-wing power generator with flow-induced pitch-plunge phasing.
Invention is credited to Richard A. Bradley, Maximilian F. Platzer.
Application Number | 20090121490 12/266553 |
Document ID | / |
Family ID | 40623006 |
Filed Date | 2009-05-14 |
United States Patent
Application |
20090121490 |
Kind Code |
A1 |
Platzer; Maximilian F. ; et
al. |
May 14, 2009 |
Oscillating-Wing Power Generator with Flow-Induced Pitch-Plunge
Phasing
Abstract
A new method for converting the kinetic energy of wind or water
flows into electric energy, comprising wings or sails which are
mounted on swing arms or on guide rails in such a way that the air
or water flow induces an oscillatory wing or sail motion with a
phase angle between the wing's or sail's pitch and plunge motion of
about ninety degrees. Stroke reversal of the oscillatory motion is
initiated by a purely aerodynamic/hydrodynamic mechanism such that
the air or water flow induces a pitching moment on the wing or sail
which rotates the wing or sail and thereby reverses the lift acting
on the wing or sail.
Inventors: |
Platzer; Maximilian F.;
(Pebble Beach, CA) ; Bradley; Richard A.; (Carmel
Valley, CA) |
Correspondence
Address: |
Maximilian F . Platzer
3070 Hermitage Road
Pebble Beach
CA
93953
US
|
Family ID: |
40623006 |
Appl. No.: |
12/266553 |
Filed: |
November 7, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61002883 |
Nov 13, 2007 |
|
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|
Current U.S.
Class: |
290/55 |
Current CPC
Class: |
Y02E 10/20 20130101;
F03B 17/065 20130101; F05B 2260/50 20130101; Y02E 10/30 20130101;
F05B 2260/40 20130101; F03B 17/06 20130101; Y02E 10/70 20130101;
F03D 5/06 20130101; F03B 17/00 20130101 |
Class at
Publication: |
290/55 |
International
Class: |
F03D 9/00 20060101
F03D009/00 |
Claims
1. For use in generating electrical energy from air or water flows,
apparatus comprising: a base plate, a swing arm and a wing or sail,
where the wing or sail is mounted on the swing arm in such a way
that it is aerodynamically or hydrodynamically unstable, thus
generating a force which causes the swing arm to move; the motion
being reversed by the generation of an aerodynamic or hydrodynamic
pitching moment at the end of the stroke which rotates the wing or
sail and generates an aerodynamic or hydrodynamic force to drive
the wing or sail in the opposite direction, thereby inducing an
oscillatory motion of the swing arm by purely aerodynamic or
hydrodynamic means.
2. For use in generating electrical energy from air or water flows,
apparatus comprising: a guide rail and a wing or sail, where the
wing or sail is attached to the guide rail in such a way that it
can glide back and forth on the guide rail. The wing or sail is
mounted in such a way that it is aerodynamically or
hydrodynamically unstable, thus generating a force which causes the
wing or sail to move along the rail; the motion being reversed by
the generation of an aerodynamic or hydrodynamic pitching moment at
the end of the stroke which rotates the wing or sail and generates
an aerodynamic or hydrodynamic force to drive the wing or sail in
the opposite direction, thereby inducing a large-amplitude
translatory oscillation of the wing or sail by purely aerodynamic
or hydrodynamic means.
3. Apparatus as claimed in claim 1 in which the pitching moment at
the end of the stroke to initiate stroke reversal is generated by
the rotation of the wing or sail around a point as shown in the
drawings and description further below or by other state-of-the-art
aerodynamic or hydrodynamic means, such as control surfaces mounted
on the wing or sail and actuated at the proper time.
4. Two apparatuses as claimed in claims 1 or 2 connected together
in such a manner that one wing or sail is at the middle of the
power stroke while the other is at the end of the stroke, thereby
achieving a self-starting smooth operation of both apparatuses.
5. Two apparatuses as claimed in claim 1 connected together in such
a manner that the individual wings or sails are oscillating in
counterphase, thereby producing a dynamically balanced system.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates in general to wings and sails, and in
particular to wings and sails which oscillate in such a way that
they convert the energy of flowing air or water into electrical
energy.
[0003] 2. Discussion of the Related Art
[0004] The phenomenon of wing flutter is well known to aeronautical
engineers, whereby an aircraft wing may experience catastrophic
failure in a few seconds due to the fact that the wing may absorb
energy from the air flow. This type of flutter usually requires
that the wing is free to oscillate in at least two degrees of
freedom, say in bending and torsion. It follows that if an airfoil
is mechanically coupled in pitch and plunge it can extract energy
from the flow. This is shown in FIG. 1.
[0005] It is feasible to construct an oscillating wing power
generator for the purpose of extracting useful power from a flow.
In 1981, McKinney and DeLaurier built such a device at the
University of Toronto which they described in the Journal of
Energy, Vol. 5, No. 2, pp. 109-115, "The Wingmill: An
Oscillating-Wing Windmill". It consists of a horizontally mounted
wing whose plunging motion is transformed into a rotary shaft
motion. The wing is pivoted to pitch at its half-chord location by
means of a fitting which is rigidly attached to the vertical
support shaft. Also fixed to the support shaft is the outer sleeve
of a push-pull cable whose end pivots on a wing-fixed lever to
control the wing's pitch. The up-and-down motion of the support
shaft is transformed, through a Scotch-yoke mechanism, into a
rotary motion of a horizontal shaft. This shaft, in turn, operates
a crank at its far end which actuates the previously mentioned
pitch-control cable. Hence the wing's pitching and plunging motions
are articulated together at a given frequency and phase angle. Wind
tunnel tests of this device showed that this type of power
generator is capable of converting wind energy into electricity
with an efficiency approaching that of conventional windmills.
[0006] In recent years, K. D. Jones, S. T. Davids, M. F. Platzer
and K. D. Jones, K. Lindsey, M. F. Platzer built similar wingmills
for use in water flows which they described in the Proceedings of
the 3.sup.rd ASME/JSME Joint Fluids Engineering Conference, San
Francisco, July 1999 and in the Proceedings of the Second
International Conference on Fluid Structure Interaction II, WIT
Press 2003, pp. 73-82, respectively. They showed that this type of
power generator is capable of converting water flow energy into
electricity. Furthermore, the company Engineering Business Ltd in
Riding Mill, Northumberland, England, built and tested an
oscillating-wing hydropower generator, called "Stingray", which
produced an output of 150 kW. They also performed computations
which showed that optimum power extraction performance requires
large plunge amplitudes (of the order of the wing chord) and large
pitch angles (70 to 80 degrees).
[0007] These prior art oscillating-wing power generators have the
disadvantage of requiring a rather elaborate mechanism to enforce
the wing's pitch-plunge motion at the proper phase angle between
the pitch and plunge motions.
[0008] Very recently, O. J. Birkestrand's application for a
"fluid-responsive oscillation power generation method and
apparatus" was published on 26 Jun. 2008 in U.S.2008/0148723. In
this invention an airfoil is mounted on a shaft such that the
airfoil can be excited into a pitch oscillation about an axis at or
close to the leading edge by actuating a trailing-edge flap. D. C.
Morris' international patent application WO 2006/093790 for an
"oscillating fluid power generator" was published on 8 Sep. 2006.
He, too, proposes the use of a single or multi-element airfoil
which pivots about a vertical mast. These recent inventions
overlook the need for a large amplitude oscillatory plunge motion
(typically of the order of one wing chord length) in order to
achieve optimum performance.
SUMMARY OF THE INVENTION
[0009] Accordingly, the present invention retains the ability to
produce large amplitude combined pitch-plunge oscillations of a
wing with a phase angle of approximately 90 degrees between the two
oscillations. However, the previously described mechanical system
to enforce this phase angle is replaced by a system which requires
no elaborate mechanism to enforce the wing's pitch-plunge motion at
the proper phase angle between the pitch and plunge motions. This
is made possible as follows:
[0010] Consider a wing which is mounted on a swing arm which, in
turn, is supported by a bearing, thus allowing the swing arm to
oscillate about the bearing axis with a finite angular amplitude.
Furthermore, the wing is mounted on the swing arm in such a way
that the wing can pitch about a pitch axis perpendicular to the
swing arm. This pitch axis is chosen to be downstream of the wing's
mid-chord point so that the wing's lift force always generates a
moment about said pitch axis which tends to increase the pitch
angle. It is well known that a symmetric wing (with zero camber)
set in a flow at zero angle of attack induces a drag force in the
flow direction but no lift force perpendicular to the wing. If the
wing is forced to move, say to the right, then an angle of attack
and therefore a force is induced which opposes the motion. However,
if the wing is set at a large positive pitch angle prior to the
motion to the right, a lift force to the right is induced. This
lift force will be decreased due to the wing's motion to the right,
but the motion to the right will continue as long as a net force to
the right is maintained by keeping the wing's pitch angle
sufficiently large. Hence work is done by the fluid on the wing
during its motion to the right. This same effect occurs during the
reverse stroke to the left if the wing is set at a sufficiently
large negative pitch angle at the start of the reverse stroke. At
the right stroke end point therefore the wing pitch angle must be
reset as quickly as possible from a relatively large positive pitch
angle (typically between 50 to 80 degrees) to a negative pitch
angle of the same value and at the end of the stroke to the left it
must be reset from the negative pitch angle to the positive pitch
angle.
[0011] The setting and maintenance of the required large positive
or negative pitch angles during the right and left strokes,
respectively, is accomplished by restraining the wing from
exceeding the desired pitch angle by physical contact between the
wing and a suitable contact surface. Furthermore, the wing will
always be pressed against the contact surface, thus maintaining the
desired pitch angle, because the pitch axis is located downstream
of the mid-chord point and therefore a hydrodynamic or aerodynamic
moment is generated which tends to turn the wing to its maximum
possible pitch angle. Hence no separate mechanical system is
required to enforce the proper pitch angle during the wing
oscillation.
[0012] It remains to reset the pitch angle as quickly as possible
at the stroke ends. This is again accomplished with the help of the
water or air flow rather than by a mechanical system. To this end
two switching rods are mounted in such a way that a spike attached
to the wing leading edge starts to touch the right or left
switching rod at the end of the right and left strokes,
respectively. This forces the wing to rotate about the switching
rod because an aerodynamic or hydrodynamic pitching moment is
generated which changes the pitch angle from positive to negative
on the right end of the stroke and from negative to positive on the
left end.
[0013] Tests of a prototype power generator in water and air
verified the feasibility and practicality of the above described
flow-induced oscillation mechanism. They also confirmed the
computational predictions of M. F. Platzer, J. Young, J. C. S. Lai,
ICAS Paper 2008-1.5.1 "Flapping-Wing Technology: The Potential for
Air Vehicle Propulsion and Airborne Power Generation", 26.sup.th
Congress of the International Council of the Aeronautical Sciences,
Anchorage, Ak., 14-19 Sep. 2008. In this paper it was shown that
flow-induced oscillation produces a greater power output per cycle
than mechanically-induced oscillation. This is due to the fact that
flow-induced oscillation produces a trapezoidal pitch amplitude
variation during the cycle in contrast to the sinusoidal variation
enforced by mechanically enforced oscillation.
[0014] An alternative way of obtaining a large amplitude plunge
(translatory) oscillation of the wing is obtained by replacing the
swing arm by a guide rail. In this version the wing is hung
vertically down from a horizontal guide rail by means of a sleeve
so that the wing can glide along the rail. As in the swing-arm
configuration, the wing can pitch about an axis located at or near
the mid-chord point and the required large positive or negative
pitch angles during the right and left strokes are enforced by
physical contact between the wing and a suitable contact surface in
a manner quite similar to the one used for the swing-arm generator.
Also, stroke reversal is initiated in a similar fashion by
attaching switching rods at the ends of the guide rail.
[0015] In summary, the proposed oscillating-wing power generator is
fundamentally different from previously demonstrated
oscillating-wing power generators because no mechanical linkages
are needed to induce a self-excited oscillation. Instead, the
needed phase angle between the pitch and plunge oscillations of the
wing is produced by purely aerodynamic or hydrodynamic effects.
[0016] Those skilled in the art will envision other aerodynamic or
hydrodynamic methods to generate the aerodynamic or hydrodynamic
forces and moments necessary to initiate the stroke reversals
described above, for example by means of control surfaces mounted
on the wing. Furthermore, those skilled in the art recognize that
the device described in the FIGS. 1 through 9 works equally well if
the wing or sail is mounted horizontally instead of vertically.
[0017] A further advantage of the proposed configuration accrues
for operation as a hydropower generator because the only part
exposed to the water flow is the wing. All other parts, in
particular the swing arm or the guide rail, are above the water
surface. Furthermore, the hydropower generator can be mounted on a
floating platform which is anchored in the tidal or river flow.
Hence, the installation effort and the environmental impact are
minimal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a foil, exposed to an air or water flow, which can
oscillate in two degrees of freedom, namely a plunge
(translational) oscillation perpendicular to the flow and a pitch
oscillation about a horizontal axis on the foil. In the upper part
of the figure the two oscillations occur with a ninety degree phase
angle, in the lower part the phase angle is zero. For the 90 degree
phase angle case the lift (unshaded arrows) is always in phase with
the motion (shaded arrows) and hence work is done by the air or
water on the foil. In the case of zero phase angle the lift opposes
the motion over parts of the cycle and the total work done is zero.
It is the purpose of this figure to explain the need for a combined
pitch and plunge oscillation and the importance of the proper
phasing between the pitch and plunge oscillations.
[0019] FIG. 2 is a diagram of the base plate and two arms 1. At the
end of the two arms two rods 2 are attached. It is the purpose of
these two rods to initiate the stroke reversal of the wing. These
rods therefore are denoted as "switching rods".
[0020] FIG. 3 is a diagram of the T-shaped swing arm 3. The axle 4
at one end of the swing arm enables the swing arm to oscillate
about a vertical axis at the center of the base plate, indicated by
the hole in the base plate shown in FIG. 2. Near the other end of
the swing arm there is a hole, indicating the pitch axis of the
wing. Also, at the ends of the T-bar two rods 5 are attached. It is
the purpose of these rods to limit the pitch angle of the wing.
These rods therefore are denoted as "pitch control rods" 5.
[0021] FIG. 4 is a diagram of the wing 6, together with an axle 7
located at a point in excess of one half chord length from the
leading edge. It is the purpose of this axle to enable the wing to
rotate about the hole shown on the swing arm to a pitch angle
limited by the pitch control rods. Also, the upper end of the wing
leading edge is extended with a spike 8. It is the purpose of this
spike to engage the switching rods for the purpose of initiating
the stroke reversals.
[0022] FIGS. 5 to 9 show the operation of the swing-arm and of the
rail-guide versions of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0023] The essence of the proposed new power generator can be
understood from FIGS. 5 and 6. The generator consists of the
following parts: the base plate with the two support arms 1 and the
two switching rods 2, the swing arm 3 with the axle 4 and the two
pitch control rods 5, the wing 6 with the pitch axle 7 and the
spike 8.
[0024] The principle of operation is as follows: The swing arm 3
oscillates about a vertical axis, indicated by the hole on the base
plate 1, with an angular amplitude which is limited by the location
of the switching rods 2. At the other end of the swing arm the wing
5 is attached to the swing arm 3 by means of the axle 4 so that it
can pitch about an axis perpendicular to the swing arm and the base
plate. At the end of each clockwise and counterclockwise stroke the
wing 6 must be rotated quickly to the proper pitch angle. Denoting
a pitch angle where the wing's leading edge points to the right as
positive the wing must be set at a positive pitch angle during its
right stroke so that a lift is generated which points right. The
air or water flow is assumed to be parallel to the two legs of the
base plate in the direction toward the axis of the swing arm. Since
the wing's pitch axis is placed at a sufficiently far downstream
location a moment is generated which deflects the wing to its
maximum possible pitch angle. This maximum pitch angle is
determined by the location of the pitch control rods 5. At the end
of the clockwise stroke the wing pitch angle must be reset to a
negative pitch angle of the same magnitude so that the wing is
pushed to the left. This switching action is accomplished by
physical contact between the spike 8 on wing 6 and the switching
rod 2 on the right support arm. As a consequence, a hydrodynamic or
aerodynamic moment is generated which rotates the wing 6 to its
maximum negative pitch angle and thus initiates the
counterclockwise stroke. Note that during the clockwise or
counterclockwise stroke the wing is set at a sufficiently large
pitch angle to generate a lift force which always points in the
direction of the motion, hence transferring work from the water or
air stream to the wing. This pitch angle is maintained throughout
the stroke because the pitch axis is located downstream of the
mid-chord axis, hence the wing 6 generates a hydrodynamic or
aerodynamic moment about the pitch axis which forces the wing 6 to
touch one of the pitch control rods 5. The distance between the two
pitch control rods 5 determines the wing's pitch angle, whereas the
distance between the two switching rods 2 determines the stroke
amplitude.
[0025] FIG. 5 shows the wing during the middle of the clockwise
stroke. Note that the wing touches the right pitch control rod
5.
[0026] FIG. 6 shows the wing toward the end of the clockwise stroke
as it starts to touch the right switching rod 2 to initiate stroke
reversal.
[0027] FIG. 7 shows the wing at a somewhat later time during the
stroke reversal at the right side.
[0028] FIGS. 8, 9 and 10 show the guide-rail version of the
invention. The swing arm is replaced by the rail guide.
[0029] FIG. 8 shows the wing during the middle of the clockwise
stroke. Note that the wing is fully deflected in pitch, touching
the right pitch control rod 5.
[0030] FIG. 9 shows the wing toward the end of the clockwise stroke
as it starts the right switching rod 2 to initiate the stroke
reversal.
[0031] FIG. 10 shows the wing shortly after the start of the return
stroke.
* * * * *